Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $223.48   7.207%   $239.5862   $239.59   $239.60   $239.60  
  Purchase #2 $177.87   5.671%   $187.957   $187.96   $187.95   $188.00  
  Purchase #3 $151.59   11.444%   $168.938   $168.94   $168.95   $168.90  
  Purchase #4 $209.60   5.510%   $221.149   $221.15   $221.15   $221.10  
  Purchase #5 $241.37   4.114%   $251.3   $251.30   $251.30   $251.30  
  Purchase #6 $231.31   5.209%   $243.3589   $243.36   $243.35   $243.40  
  Purchase #7 $173.60   7.273%   $186.2259   $186.23   $186.25   $186.20  
  7 purchase totals = $1,408.82       $1,498.5150   $1,498.53   $1,498.55   $1,498.50